Is That Melanoma Deadly?

Treatment
The prevailing veterinary opinion is that melanomas should be considered incurable and that benign neglect is the best treatment approach, until and unless problems arise. To the extent that melanomas in aged gray horses likely represent a body-wide change/abnormality in production and/or handling of melanin, that is probably correct. However, some of the prevailing wisdoms regarding melanoma should be re-examined.

You may have heard that surgical removal of melanomas is dangerous and triggers spread. However, a search of the literature does not support that idea. While it's true that melanomas with particularly malignant features may exhibit explosive spread if disturbed by a surgery, this is apparently a rare occurrence with melanomas. As a safeguard, needle aspiration of the tumor for cytology can be done prior to surgery.

Surgery is usually only considered if a tumor becomes a problem in its location, e.g. is interfering with function or is ulcerating. However, it's also an option for horses who have only one or two tumors and is usually curative. In horses with multiple tumors, surgery can be considered for only the ones that are causing problems. Tumors that have ulcerated or are causing problems because of their location can also be effectively reduced by cryotherapy (freezing), although this is not curative.

Otherwise, there are few treatment options. Melanomas respond poorly, if at all, to radiation and chemotherapy. Based on work with human melanomas, vaccines have been suggested but have not produced exciting results to date. The antiulcer drug cimetidine (Tagamet) apparently causes tumor shrinkage for variable time periods in some horses, and in others does not work at all. Immunotherapy showed promising results in one trial, but we're a long way away from having this be an option.